I have to check my book shelf (at home, where I am not at the moment) to give complete citations, but the two authors who come to mind are Morton Cohen and Collingwood. Both wrote books with examples, exerpts, etc. I also have a half-recollection that Mrs Hatch (Evenlyn??, Beatrice's mother) published some letters too. I thought Cohen was available via Google Books but will leave that to the inquisitive to verify.

Another source is http://books.google.com/books?id=z1g...etters&f=false